The present invention relates to a technology for enriching a sound (i.e. r, musical sound or tone) of a keyboard instrument.
Usually, an electronic piano has no soundboard unlike an acoustic piano, because the electronic piano is configured to produce electronic sound from a speaker. However, Japanese patent application laid-open publication No. JP2008-292739A discloses a technology of mounting a soundboard on the electronic piano and installing speakers on the soundboard so that by exciting the soundboard with the speakers, a vibration sound is radiated from the soundboard. As a result, the electronic piano can produce not only electronic sounds but also enriched acoustic low-pitched sounds due to radiation of the vibration sounds from the soundboard. The above-mentioned patent literature also discloses that such a technology can be applied to not only the electronic piano but also a ease where the acoustic piano is configured not to vibrate any strings (sound-deadening piano).
In order to vibrate the soundboard, voice coil type actuator is employed in which a drive force is produced by a voice coil input a drive signal thereto. Such a type of the actuator can realized at a low cost because it has a structure similar to a voice coil type speaker, and on the other hand, features of the voice coil seriously affect a drive characteristic of the actuator. For example, while an amplitude of an excited vibration increases as the length of a voice coil along a direction of the drive force increases, a responsiveness in a high frequency band is deteriorated because an inductance of the coil increases along with increment of the number of windings of the coil. Therefore, in case where the voice coil type speaker is used as an actuator for exciting the soundboard, even if a desired sound quality can be achieved when generating a sound as a speaker, a desired sound quality sometimes could not be achieved when exciting the soundboard.